This application has priority benefit of European Patent Application No. 98811233.0, filed on Dec. 16, 1998.
The present invention relates to lids for closing off containers using a sealing seam in which the lids contain a substrate material featuring , with respect to a container on which the lids are used, outward facing printing and an inward facing sealing layer.
It is known to provide containers such as deep drawn or stretch drawn containers with a ring-shaped shoulder at their opening and to lid such containers, in particular after filling, such that the lid lies over the whole of the shoulder and e.g. by sealing or adhesive bonding, to attach the lid permanently and in an air-tight manner to the shoulder.
The lids are e.g. stamped out of an endless strip of lid material and stacked. The stacks of lids are fed to a packaging machine and the individual or unstacked lids continuously sealed on to the already filled containers. The lidsxe2x80x94already featuring a sealing layerxe2x80x94are sealed onto the shoulder region of the container at the edge of the container using a sealing tool. The separation or unstacking of the lids from the stacks is not always reliably performed by the packaging machine as the stacked lids may stick to each other. It is possible to prevent the lids from sticking together, for example by embossing the lid material. Embossed patterns on the lid material, however, have a negative effect on the printed image on the outside of the lid.
The lid material can be of various different materials depending on the requirements in question. Typical examples of lid material are metal foils which may be coated with plastic on one or both sides. Other lid materials contain or comprise of plastics in the form of mono-films or multilayer laminates. Further lid materials can be of cellulose-containing materials such as cellophane or paper. Also laminates of metal foil and plastic films are employed. In order to seal the lid material to the edge of the container, the lid material is provided over the whole of its surface with a sealing layer such as an organic coating or sealing film, whereby the sealing layer is deposited at least on the side of the finished packaging facing the inside i.e. facing the interior of the container.
The lid material also serves as a substrate for information and advertising. For that reason the lid material is generally provided with printing on its outside. The printing may be on the uppermost layer facing outwards on the finished container i.e. so called first form printing. The printing may also be covered over by a protective lacquer or a protective film, or the uppermost layer may be of transparent material and bear the printing as a reverse image in the form of counter-printing. The printed images may be single or multi-coloured and may be deposited in a printing machine.
Application of an embossed image is a disadvantage with known lid materials. The embossing is necessary in order that the lids manufactured from the lid material in stacks can be fed to the packaging machine, and that the lids can even be separated piece for piece from the stack and sealed onto the container. As the lid material has to be embossed, the finished lid is at a disadvantage to reproduce the desired image.
The object of the present invention is to overcome this disadvantage and to propose a lid that can be separated into individual lids from a stack of lids, yet reproduces with high quality the image on its surface.